Oh...
That reply wasn't even intended for this thread.
Maybe I could get a Host to delete my post? LOL!
OK, there was a confusion that carried over between two posts I was looking into (and elsewhere.)
There was another thread in iBook -- that had an issue -- with different troubleshooting. So the mixup.
Then I had to drive an elder to hours-long medical appointments, just got back. Sorry about that.
Usually between this that and the other thing, I spend most days helping semi-invalid elder parent.
https://www.ifixit.com/Device/iMac_G3
A new clock battery on the logic board may help resolve some startup issues, if it is dead
or very weak. Or if the computer had a later OS X installed but the Firmware Update was
not installed first in an original Mac OS running in the computer, a symptom of this failure
is a black screen and nothing else on boot-up. Some users were able to connect external
display (on models with external port) to help troubleshoot this issue. Others not so much.
(I've only owned & repaired, then donated about 300+ Macs and then got away from that
for awhile. Most of these I've owned more than a few of, and hadn't owned a computer
prior to getting one that needed work. Then, at one time I had a room with 75 in it. but that
was never in a business or other location, just where I lived. All repaired, & working... So
it was a big disappointment for me to get a new computer with AppleCare and found there
was no Apple Store or decent authorized repair company who'd handle issues with it. And
as I wasn't certified, I could not fix it while under Apple warranty, either. I have a few that
need repair, but I don't have time now for that, or for me.)
Anyway, I'm expected to do other things, elsewhere; and so I'm going offline again.
Sorry for the mess-up in adding a reply here, that wasn't for your Mac at all...! 😝